Thesis (M.Sc.)--Chulalongkorn University, 2011

This research aims to determine the effect of citric acid modification on resistant starch content and physicochemical properties of rice flour, and to study the application of the modified rice flour in dried rice noodle. Rice flour was modified by 0.1M citric acid at different reaction temperatures (100, 110 and 120°C) and times (15, 30 and 45 min). The acid treated flour was then incubated at 5, 30, 45, 60, 75 and 90ºC. The resistant starch content and physicochemical properties of native and modified rice flour were measured. Dried rice noodles were produced with replacing rice flour by modified rice flour at 10, 20 and 30% and drying at 50, 60 and 70ºC. Resistant starch content, cooking quality and texture of rice noodle were evaluated. The results showed that the resistant starch content of rice flour increased from 0.65% (native) to 6.51% (acid treated at 120°C, 45 min). Amylose content, solubility and the amylose-lipid complex of modified rice flour were higher than those of the native flour. Treated rice flour at 100°C had higher swelling power, but swelling power decreased at higher condition. The pasting properties of acid treated rice flour showed to decrease in viscosity, breakdown and setback while those treated at the highest condition (120°C, 45 min) exhibited no RVA peak. Whiteness index and relative crystallinity of modified rice flour were lower than the native. The higher reaction temperature and time resulted in greater change in all properties except degree of crystallinity. Rice flour treated at 120°C/45 min was chosen for studying the effect of incubation temperature due to its highest resistant starch content (6.51%). After incubation, the resistant starch content, amylose content, solubility, the amylose-lipid complex, and relative crystallinity of modified rice flour increased with increasing temperature. Modified rice flour incubated at 90°C had the highest resistant starch content (12.41%). Increasing % modified rice flour resulted in higher resistant starch, cooking loss, rehydration, and springiness, but lower in hardness, tensile strength, and cutting force of noodle. The optimum % substitution of modified rice flour at 20% gave noodle having 3.0% resistant starch and the highest sensory score. Drying temperature had no effect on resistant starch content and cooking loss. However, higher drying temperature increased rehydration but decreased tensile strength, cutting force, hardness, and springiness. The suitable drying temperature was 50°C which gave noodle having the highest sensory score.